1. Technical Field
The present disclosure relates to a technique that detects biological information.
2. Description of the Related Art
As basic parameters for determining the physical condition of a human, a heart rate, a blood flow rate, a blood pressure, an oxygen saturation in blood and others are widely used. These pieces of biological information on blood are usually measured by a contact measuring instrument. Since the body of a subject is restrained by a contact measuring instrument, when measurement is continuously made particularly for a long time, discomfort of the subject is caused.
These days, due to increase of chronic disease and aging of the society, practice and diffusion of health care at home are being promoted. Because measurement of biological information conducted in medical facilities has the purpose of curing disease, a patient can bear the pain associated with the measurement. However, for the application of health care at home, diffusion of health care would be difficult if the measurement causes pain or inconvenience. A different approach not the extension of the measurement technique conducted in medical facilities is called for the measurement technique in home medical care. For instance, it is expected that measurement be made naturally in a noninvasive manner, in an unrestrained and non-contact manner, and further in an unconscious state.
Japanese Unexamined Patent Application Publication (JP-A) No. 2002-71825 discloses an example of a method of measuring biological information in a non-contact manner. The human body sensor disclosed in JP-A No. 2002-71825 measures a heart rate, a breathing rate, a body motion using microwave which is invisible to human eyes. In addition, Japanese Unexamined Patent Application Publication Nos. 2014-36801 and 2015-100432 disclose a method of measuring a pulse rate and a breathing rate based on a minute change in brightness not perceivable by human eyes, using a normal camera. Each of the measurement methods observes reflection of electromagnetic waves from a body surface to enable non-contact biological information measurement.
On the other hand, as a method of obtaining biological information on a deeper portion in a noninvasive manner, near infrared spectroscopy (hereinafter, referred to as NIRS) is known. This measurement method uses electromagnetic waves (hereinafter referred to as “light”) of near-infrared wavelength range (mainly 700 nm to 1000 nm). The light in the above-mentioned wavelength range has a relatively high transmittance through a body tissue such as muscle, fat and bones, and thus called “biological window”. In addition, the light in the above-mentioned wavelength range has the property of being likely to be absorbed by oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) in blood, and thus NIRS makes it possible to measure changes in a blood flow. NIRS is mainly used for measuring a brain function, and is applied to diagnosis of psychiatric disorders such as depression. An optical brain function measuring device to measure a brain function using NIRS irradiates a subject with near-infrared rays (also referred to as “near-infrared light”) from a light source disposed above the scalp of the subject, and detects the light which has passed through the inside of the cerebral cortex by a detector. The oxyhemoglobin concentration and deoxyhemoglobin concentration in the blood flowing through the brain can be calculated based on the signal detected by the detector. The activity state (hereinafter may be called “brain function”) of a brain can be estimated based on an oxygenation state of hemoglobin. Japanese Unexamined Patent Application Publication No. 2015-134157 discloses an example of an optical brain function measuring device that measures a brain function utilizing the NIRS.
Japanese Unexamined Patent Application Publication No. 9-19408 discloses a measurement device in which a plurality of light irradiation units and light receiving units are regularly disposed, and a spatial distribution of signals to be measured is calculated from signals detected by the light receiving units.